Search coil magnetometer attributes have been exploited for years in low frequency (i.e. usually frequencies less than 2 Hz) ferrous target sensor applications that do not require detection of absolute magnetic field (H) values, but only very small induced changes, or deltas, as the target translates by the sensors static location. Search coil magnetometers operate using a passive transducer that requires no excitation power because the time changing magnetic H field to be detected directly induces a voltage across its coil. The induced voltage varies in accordance with the formula E=KdH/dt, where E is voltage, H is the magnetic field strength and K is the coil sensitivity, usually expressed in terms of “volt-seconds per Oersted.”
Traditionally, low noise base-band front-end amplifiers, or preamplifiers, have been used to increase low coil output voltage from a search coil magnetometer to usable signal processing levels. Such traditional approaches employ complex chopper stabilized amplifiers and low-frequency base-band preamplifier designs in various low-noise configurations and topologies. Conventionally, low pass filtering is employed to flatten and band-limit coil output signal rate characteristics (dH/dt) in order to preserve in-band dynamic range capabilities. A dominant pole is often incorporated directly at the coil using the coil's output resistance. Unfortunately, base-band preamplifiers exhibit a significant level of 1/f noise, which significantly degrades system sensitivity at the lowest frequencies of interest, which are often 0.1 Hz or less.
In contrast to conventional approaches, the present invention provides a less complex sampling low noise front-end amplifier architecture that substantially eliminates 1/f noise problems prevalent in traditional base-band low noise preamplifiers. As a result, improved sensor performance is essentially limited only by noise generated by the transducer coil winding(s), or bridge element(s).
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. § 1.56(a) exists.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention, a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Preferred Embodiments below.
A brief abstract of the technical disclosure in the specification is provided as well for the purposes of complying with 37 C.F.R. § 1.72.